• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

DIY bluetooth speaker

i am not trying to say you dont deserve better stuff, i am just saying the friends who ask me for diy speaker arent the ones who are ready to spend 300$ on a JBL. My price is very cheap, as it is, its almost charity from my side. But if a person is only ready to spend x amount of money, then i cant buy speakers that cost 10x. If i were doing a speaker for myself, that would be a different thing, budget there would be at least 4x higher.

As for no debt, cudos. I also have no dept and have a fair amount of money stored away, probably comes with my nature, always expecting some **** to come down. But part of the reason is also that im very non materialistic - i have 10 year old pc and have no need for new one, have a cheap mobile phone that is working great. The only money i will actualy be spending is renovating my place. Aside from that, being in a workshop and trying to make something useful bring me more joy than some gadget would.

Anyway, i am in the process of making another BT speaker, this time a 4L one, for the first time using Dayton TCP115 4 ohm. I am really anxious to see if i will be able to detect that 5dB difference compared to 8 ohm version. Pretty sure i wont since even 8 ohm version is so loud in the small workshop.

Also, i made a 4L case and hopefuly today i can test how that tiny visaton FR 8 work - if it actualy produces the bass that my graphs showed.
Ok so i tested the visaton fr 8 4 ohm in 4L enclosure with a port. And certanly, there is bass u can hear. Covering the port changes to no bass. But sadly it is as you predicted. The medium frequencies are so loud that u hear a lot less bass. So this would be usable only for very cheap BT speaker, sadly, cheap speakers must be compact and 4L is huge. So we can end the discusion of using this speakers without woofer in any system.

I have still to decide whether they sound good enough to be a speaker covering medium to high frequencies. I will keep testing different gear until i find something i am satisfied with :)
Well, on some other forum they gave me a link to tweeter from Dayton which is supposed to be quite OK, at least compared to aliexpress one for 4$. It costs like 9€ but i think i can handle that. I kinda like dayton and so, why not order from them:


Ok a quick question here. Port. I do it all right. Calculate port volume, then add this volume to enclosure size in the end. But 1 thing i never did is account for port thickness. Right now its 1mm. Do you guys add this also to the calculation ? Its prolly not enough volume to add much to the enclosure size but im just wondering how "far" you go in trying to make it as precise as possible. Reason im asking is, i found a great plastic pipe in my basement and its just about the right size for the port (about 3cm diameter), but its about 2 or 3mm thick. So next time i guess i will add that volume to the equation. Meaning instead of 3cm diameter i will say ok, inner diameter is 3cm so thats what the port is. BUT, when i calculate how much enclosure i must add because of the port, i will actualy use 3.1cm or 3.2cm.


Well-Known Member
Most Helpful Member
The Dayton tweeter has a nice flat frequency response but its max allowed power is only 10W. I hope it will survive if somebody turns up the volume so the amplifier produces severe high frequency distortion.

The thickness of the port must be enough for it not to flex. The entire volume of the port is much more than its thickness. Then the volume of the thickness is negligible.
Good to hear about the dayton tweeter. Yes, i hope it will survive, we will see. Btw, remember when i told you about customer who said, hes happy with speaker but would also buy from me a bigger - louder speaker ? So i have been looking into that. One thing is clear, i cannot up the wattage much more, if i want him to have decent battery life. So its about sensitivity, which means bigger speaker. Since limit for woofer is 30€, i went check that out. I found multiple nice woofers but watch this woofer and how flat the line is, while still going low enough for my needs:

In the attached image u can see the line is almost completely flat. It has a whooping 92.1dB at 4 ohms. For comparison dayton tcp115 4 ohm has 86.8dB at 4 ohms. That is 5.3dB difference which translates to about 45% more loudness. I am pretty sure u can notice that. And remember, the person right now is using tcp115 8 ohm version, which has 81.9dB. So if u combine all that, he will hear almost 10dB difference in loudness. If data is correct ofcourse. What do u think ?



Well-Known Member
Most Helpful Member
The woofer has pretty good bass but it has cone breakup above 2.5kHz causing it to have some shrieking in the sound.
Parts Express has a much lower price than you found.
Yeah but sadly parts express has ridiculous shipping costs for me since im in central europe. Sound imports has very low shipping cause its much nearer. I only gave this woofer as an example, i will keep searching and might even find something better and cheaper. But its just good to know that i still have headroom in improving loudness.
I am making a louder speaker for that person, he said size isnt an issue. My woofer budget is 30 euro/dollar, tweeter about 15. So people suggested me this speaker:

I calculated it and will go to about 65Hz in 15L enclosure and has magnificent sensitivity. Any other alternatives ?
I have an interesting thing to report. First of all, i know i cant measure my amplifier power draw by killawatt and multimeter since music is to fast for it. BUT. I made another speaker, with 2x50W amp, TCP115 4 ohm and tweeter. Now i tested this speaker with the 50W amp and went through some songs at maxximum volume and came to about 40W of usage, i only saw 50W in that extreme bass boosted song.

OK, so we say tweeter + woofer are about 50W together. Coming from 25V power suply, that means a peak of 2A. So i went testing my batteries and all of them, when i apply a 2A load on them, have a voltage drop from 4.2V to about 3.5V. So thats 6 batteries in series which is 21V.

Ok, all fine till here. But get this. My speaker has mini voltage display connected to the same power as my amplifier. So i am literaly measuring the voltage that goes into the amp. And when i crank the same music to maximum volume, the voltage barely change. Sometimes it goes down by about 0.2-0.5V, so that would mean going from 25.5V to 25.3V or 25V.

Now do you see where my problem is ? I calculated max power draw of amp. I took the single battery and stressed it with the same amperage and i saw a huge voltage drop. Why do i not see the voltage drop when my speaker is playing ? Judging by single cell drop at 2A, it should be at 21V, not 25V. Now i know what ur going to say, multimeter is not fast enough. But, when i stop the music, voltage actualy stays almost the same or within 0.5V.

Ok, so the only thing i can think of is ...with killawatt i measured like this: connected DC power suply to amplifier and put the other end into killawatt. So for some reason killawatt was able to detect those big power surges of the bass and that is why it stayed at 40W usage most of the time. But this little digital multimeter, it simply wasnt able to detect those peaks. So even if it shows 25V in reality its dropping down to 21V everytime bass hits, but its to slow to record it. Is this the explanation ?


Well-Known Member
Most Helpful Member
Maximum volume does not mean full power. If the input signal level is high and the amplifier has lots of extra gain for you to be able to turn up some faint music then the amplifier will produce 50W plus maybe another 30W of severe distortion.
But if the amplifier has less gain than you need its output power is less than its maximum undistorted rating

The amplifier has some large capacitors in parallel with the battery that charge between music peaks then discharge a lot of current but with less voltage drop than the battery does during each full power peak.
Hmmm. The capacitors. But, the test was same both with external DC power and with batteries, in both cases there was amp with the capacitors. If killawatt showed 50W, using the voltage which is stable on DC power, the current was indeed 2A. And there should be the same current on batteries. And i did prove that at 2A there is significant voltage drop when i tested individual cells. So there should be the same voltage drop when using batteries, driving the amp on full power.


Well-Known Member
Most Helpful Member
On Google, I asked for an 18650 battery test and found many. This one has a guy testing genuine Samsung and LG brands and some fake ones. It is here:
The first one is a genuine Samsung cell and it had an internal resistance of 23 milli-ohms so it can produce 30.4A when its 4.2V drops to 3.5V.
Maybe your cells are old fakes or maybe their wiring is poor (battery holders have a fairly high resistance).

EDIT: I forgot to add that maybe your battery was not fully charged. It is no where near a full charge when the charging voltage of each cell reaches 4.2V. Instead it is fully charged when the voltage of each cell reaches 4.2V PLUS when the charging current drops to a low amount.
Batteries are old, from laptops.

But the fact remains, when i measure them they read 4.19V. And they remain 4.19V even when speaker is blasting on 100%. And i measured that killawatt shows 2A at 100%. And i tested batteries and they drop to 3.5V when i apply 2A resistor. So this makes no sense, 2A is 2A isnt it ? If there is voltage drop when i apply resistor to get 2A, there should also be voltage drop when the amp applies 2A, yes ?


Well-Known Member
Most Helpful Member
Music has a wide dynamic range. Your test is valid only when the amplifier is playing a continuous sinewave into a speaker at a frequency where the impedance of the speaker is in your calculations. Maybe the killawatt shows peak instantaneous power?
That is what i was thinking. That maybe killawatt only shows max, and on the other hand, that little digital voltmeter somehow cant pick up the peaks and just shows average voltage. I wish i had gear to make a proper test but sadly, i dont.

Oh and just to say why im interested in this ... i would like to know how long the speaker lasts on max volume, since everyone asks me that. The problem is that with this speaker and its brothers, if i put it to max at home, i will have police and neighbours at my door in 5 minutes. And when i am outside i usualy drink and will prolly forget how much i used it.

I do know though that my last speaker, 2x25W, cheap logitech woofer on left and full range visaton frs 8 m on right channel, with no crossover, i know that in hours of playing at max, it only went from 25.5V to about 24.5V. So i guess with my new speaker (6S2P batteries, all batteries over 2000mAh), i could play speaker outside for 1 straight hour and read the voltage. Then go check the li-ion discharge graph. It should give me some idea how much % capacity i used in that 1 hour. But i think this speaker will play for a long time, considering total battery capacity is about 24.000mAh. This will be my new personal speaker (i killed the old prototype passive membrane 1 last friday, poured to much beer into the woofer membrane and didnt know it was paper membrane - dayton tcp115 is all plastic. anyway im glad i killed it cause i was ashamed of walking around with it lol, bad commercial for my speakers xD), its about 50W peak at 100% volume. I am speculating but even at 2A draw (50W) this would mean 12 hours on max volume. But like i said, this 2A are only peaks if u ask me ... average is much lower so i think 24 hours on max volume is not out of the question, no?
Last edited:


Well-Known Member
Most Helpful Member
Your battery has two rows of 2000mAh batteries in parallel which makes it 4000mAh.
We do not know how close to maximum output power is your "100% volume".
We also don't know the average power your system is producing.
Then the battery charge might last for 10 hours.
See now i dont agree with you. All my last batteries were 6 cells in series, 2000mAh each and that would mean my battery pack is 2000mAh only. Which it is not, u cant run speaker on max for hours like that. Cells add up for higher voltage and that means for same power usage i need lower amperage.

And this time i am not standing down. If i indeed had only 2000mAh pack and knowing my speaker on max draws at least 1A, that would mean speaker would last for 2 hours. My old speaker was running for 6+ hours and only went from 25V to 24.5V. The person i sold the speaker to said his speaker lasted for 3 parties on 1 charge and each his parties was at least 5 hours.

I know i am walking on thin ice but this time i am not backing down. I belive i am right and i do indeed have a 24.000mAh pack.

As for maxximum out power that i am producing, it doesn't matter. I used the same speaker and same amp both when i tested it with DC power and with batteries. Only the power source changed, everything else was the same. And i told you, on external DC power suply, i noted a max of 40W during normal songs and about 55W on that ridiculous bass boosted song.


Well-Known Member
Most Helpful Member
I belive i am right and i do indeed have a 24.000mAh pack.
Sorry, you are wrong.
As AG states, if you have a 2P configuration with 2000mAh cells, you have a 4000mAh pack.
If you had 3P, it would be 6000mAh.
Voltage adds up with a series connection, not the current.
Current adds up with a parallel connection, not the voltage.

Using your 2000mAh cells in a 6S2P setup gives 25.2V, 4000mAh.
To have a 25.2V, 24000mAh pack, you would have to build it as a 6S12P. EDIT: That would require 72 cells...;)
But it makes no sense. What if i had 1S2P, that would mean 4000mAh pack ? Same as 6S2P ? I know current doesn't add up, voltage does. But if i wanted to run the speaker at 50W with 1S, i would need 50A of current which means battery would die very soon. If i have 6S 25V, then because of higher voltage the current needed for 50W is only 2A and that means the batteries will last a lot longer.


Well-Known Member
Most Helpful Member
Play a continuous 400Hz tone at 50W into 4 ohms (39.9 p-p, the amplifier is bridged) and see the amplifier get very hot and the 2p battery last for a little less than 2 hours.
When the loudest parts of music are almost clipping then the 2p battery will last for 10 hours to 20 hours.

50W from a 4.2V battery needs a current of more than 11.9A (the extra current heats the amplifier) and the speaker impedance must be 0.35 ohms.

Latest threads

EE World Online Articles